How to add user to custom group upon registration
 

I'm trying to use an email filter..if they have an acceptable email address they are a regular user and if they don't they get put on a restrictive usergroup.

How do I assign a usergroup at registration?

The best way is to have the default group 'Registered Users' be the restrictive usergroup, and then set promotions to move them to other, less restrictive groups.

ok, but I want the process to be automated so I don't have to manually sort people out.

It is an automated process after you have the promotions set up. Once an hour, vB checks the promotions and promotes the user automatically (it could take up to one hour after they register).

As an example, I have the Registered Users group set up so that all new threads/posts go to the moderation queue, so I can check them for spam (I don't do it manually, I use an akismet plugin :) ). Then I have a promotion set up for when a user has a minimum of 5 posts and 2 days of being registered, they are automatically sent to another group that doesn't have this restriction. I think you could do the same, just have the parameter be their email address instead of their post count.

Have a look at this ;

https://vborg.vbsupport.ru/showthread.php?t=112559